1. Field of the Invention
The present invention relates to a two-terminal microelectronic device, and, in particular, to a two-terminal non-volatile resistor device, having a structure of electrode/active-resistance change material-layer/electrode, which is an Electric-Pulse-Induced-Resistance change device, commonly referred to by the acronym EPIR.
2. Description of the Related Art
The electric resistance of transition metal oxides and solid state electrolyte materials can be modified by applying one or more short electrical pulses to a thin film or bulk material. The electric field strength or electric current density of the pulse is sufficient to switch the physical state of the materials so as to modify the properties of the material. The pulse is desired to have low energy so as not to destroy the material. (S. Q. Liu, N. J. Wu, and A. Ignatiev, Applied Physics Letters, 76, 2749 (2000).) Multiple pulses may be applied to the material to produce incremental changes in properties of the material (S. Q. Liu, N. J. Wu, and A. Ignatiev, as disclosed in U.S. Pat. Nos. 6,204,139, and 6,473,332, which are incorporated herein by this reference). One of the properties that can be changed is the resistance of the material. The change may be partially or totally reversible using pulses of opposite polarities. This has been defined as the electrical pulse induced non-volatile resistance change effect, abbreviated as the EPIR effect. Based on the EPIR effect, a two terminal non-volatile resistor device, having a structure of electrode/active-material-layer/electrode, can be produced, and is called an EPIR device.
As an example, it has been shown in the paper “Evidence for an Oxygen Diffusion Model for the Electric Pulse Induced Resistance Change Effect in Transition-Metal Oxides” by Nian et al., Physical Review Letters, The American Physical Society, PRL 98, 146403-1 to 146403-4 (2007), that for an electrode-perovskite oxide-electrode device under applied voltage pulses across the device, the motion of oxygen ions/vacancies and their pile-up at the perovskite oxide-electrode interface region is responsible for the EPIR effect. The changing concentration of vacancies within this interface region affects the conductivity of the perovskite oxide and results in resistance change. This change in concentration, however, results in a chemical potential gradient which under certain conditions can become a driver in changing the concentration of oxygen ions or vacancies between the interface region and the bulk, thus changing the resistance state of the device and yielding poor retention. What is needed is an EPIR device that is constructed to mitigate the retention challenge.